This is a very hard question to answer. Online casinos are always adding more games and the casino that offer the highest numbers of games today might not be the casino that offers the highest number of games tomorrow. Generally speaking however it can be said that a casino that offer games from a large number of different developers usually also offer a large number of games.
The number of games is usually not relevant. A lot of the games in many casinos are not very good and do not offer much extra value to a player. A casino that offer 100 god games is a better choice than a casino that offer 1000 games of which only very few are good. Your goal should not be to find a large selection of games but rather to find a good selection of games.
If you want to find a casino with a good selection of games you should look for a casino that fulfills the following criteria.
The casino should co-operate with a large number of different game developers. The more developers they co-operate with the better selection of games they can offer. The most important developers that a casino should co-operate with are NetEntertainment and Microgaming. These two developers have developed many of the most popular slot games.
Other smaller developers that offer good games includes Yggdrasil, RabCat, NextGen and many more.
Look for a casino that co-operates with both NetEntertainment and Microgaming as well as a number of small developers.